Stretcher frame for artist{3 s canvas

ABSTRACT

Four plastic stretchers, two each being of the same length, are assembled together in rectangular shape. A plurality of inwardly diverging fastener-receiving holes are provided along the outside edges of all four stretchers when so assembled so that an artist&#39;&#39;s canvas can be stretched over the frame, and rivet-like fasteners forced down through the canvas and into each of the fastener-receiving openings to maintain the canvas in place on the frame. Plastic wedges are forced into grooves provided at the junction of each pair of stretchers to force the tongues of adjacent stretchers away from each other, thus stretching the canvas on the frame. Bumps on flat opposed surfaces of the wedges are thus brought into interfering relation with flat boundary surfaces of these grooves to develop substantial positive forces locking the wedges in position in the grooves. Alternatively, in place of rivet-like fasteners in fastenerreceiving openings, outer edges of each of the stretchers are channelled out and a soft plastic or hard felt materials is embedded therein. Staples are forced through canvas over the edges of the frame and into these embedded materials to hold the canvas in its proper place on the frame.

United States Patent Starzyk 1 May 13, 1975 STRETCHER FRAME FOR ARTISTS length, are assembled to ether in rectangular sha e. A

CANVAS plurality of inwardly diverging fastener-receiving holes are provided along the outside edges of all four [76] Inventor' f g f sz g stretchers when so assembled so that an artists canvas p can be stretched over the frame, and rivet-like fasten- [22] Filed: July 31, 1974 ers forced down through the canvas and into each of 21 Appl. No.: 493,241

[52] US. Cl 38/l02.l; 160/374.1 [51] Int. Cl. D06c 3/08 [58] Field of Search.... 38/102, 102.1, 1024, 102.5, 38/1029, 102.91; 160/371, 374.1, 378, 380, 382, 383, 390-393, 398, 404; 69/19.119.3

[56] References Cited UNITED STATES PATENTS 1,128,362 2/1915 Rawbou l60/374.1 1,847,925 3/1932 Carter 160/374.l 1,916,022 6/1933 Shull l60/374.1 3,422,554 1/1969 Prinzhom 38/1021 Primary ExaminerGeo. V. Larkin [57] ABSTRACT Four plastic stretchers, two each being of the same the fastener-receiving openings to maintain the canvas in place on the frame. Plastic wedges are forced into grooves provided at the junction of each pair of stretchers to force the tongues of adjacent stretchers away from each-other, thus stretching the canvas on the frame. Bumps on flat opposed surfaces of the wedges are thus brought into interfering relation with flat boundary surfaces of these grooves to develop substantial positive forces locking the wedges in position in the grooves.

Alternatively, in place of rivet-like fasteners in fastener-receiving openings, outer edges of each of the stretchers, are channelled out and a soft plastic or hard felt materials is embedded therein. Staples are forced through canvas over the edges of the frame and into these embedded materials to hold the canvas in its proper place on the frame.

8 Claims, 10 Drawing Figures 1 11111 I 3 I ll' 3 -76 HI'" li lll' llllll ulu.

1min illll l glll'llIl STRETCHER FRAME FOR ARTISTS CANVAS BACKGROUND OF THE INVENTION Stretcher frames for artists canvases have long been made of wood. Customarily these frames consist of four wooden stretchers, two each being of the same length, fastened together at the adjacent corners, with the artists canvas stretched over the four outer edges of the frame and fastened to the frame by staples or headed nails or the like. Customarily wedges are provided which can be forced into grooves at the corners of the frame to bear on tongues in the grooves to force the stretchers outwardly with respect to each other to obtain the necessary and desirable tension on the canvas. Once a painting is completed on such a canvas, customarily it remains permanently on the frame, and the frame is never used again except to position this particular piece of canvas for the entire existence of the painting on the canvas, whether this be one month, one year, or one hundred years. Thus wood allocated to the production of such stretcher frames is customarily used but once and is forever lost.

Several saw cuts and routing procedures must be utilized in order to produce wooden stretchers for the manufacture of such stretcher frames, thus making the resulting frame a relatively expensive article. Further, the kind of woods most readily adaptable for producing such frames are currently in very limited supply.

Where a particular stretcher frame is used over and over, as in art school or the like, the continual driving of staples or nails into the outer edges of each of the stretchers soon renders the stretcher unsuitable for further use because there are no sound positions where staples or nails can be driven.

Flat wooden wedges to drive adjacent mating stretchers away from each other to stretch the canvas have been utilized fairly effectively, but they are difficult to produce and easy to break, and both the stretcher frame and the wooden wedge are susceptible to drying and shrinking and becoming moist and swelling, thus changing the tension on the canvas on a particular frame. To overcome some of these difficulties, plastic wedges having small individual bumps on both outwardly facing surfaces thereof have been utilized in connection with wooden stretchers, and the sizes are such that these bumps actually dig into the parallel facing surfaces-of the grooves in these stretchers as they are driven in to move the stretchers away from each other to bring the canvas into taut relationship. These bumps actually cause tracks to be formed in the facing surfaces of grooves of the stretchers, and these tracks do not entirely come out of the wood when the stretcher is removed, so that repeated use of plastic wedges in grooves on wooden stretcher frames which are used over and over sooner or later renders these stretchers unsuitable for use as the friction between the bumps on the wedges and stretcher grooves decreases through this repeated usage.

BRIEF SUMMARY OF THE INVENTION To overcome the difficulties in the prior art as described above, the stretcher frame of the present invention was developed.

Stretcher frames for artists canvases made according to the present invention include four plastic canvas stretchers, two each being of the same length, the four being fitted together to form a rectangular frame. In' a first form of the invention, inwardly diverging openings extend from outer edge surfacesof each of the stretchers inwardly; and rivet-like fasteners are provided which will be of configuration to force their way through outer edges of a canvas which has been placed over the frame and in to these openings thus to hold the canvas in position on the frame.

Plastic wedges are provided to be positioned between end grooves in each stretcher and an outer tongue edge of the adjacent stretcher, and the parts are of configuration so that forcing of the wedges into these slots will tend to force the adjacent ends of mating stretchers slightly away from each other to the end that the canvas is properly stretched and tensioned for use by the artist.

In a second form of the invention, channel-like openings are provided in the outer edges of each stretcher, and soft plastic or hard felt is embedded in these openings. In this form of the invention, staples or headed nails can be forced through the edges of the canvas after the canvas is in position on the frame, thus to permanently hold the canvas in position relative to the frame.

In both forms of the invention as shown, all surfaces of each of the stretchers taper from outside to inside in direction such that the stretcher can be removed from its mold in direction from the inside toward the outside in the process of manufacture. In one form of the invention, the parts can be manufactured by injection molding. Many plastic materials will be suitable for forming stretcher frames of the present invention, but a thermo plastic material manufactured by General Electric Company and identified by its trademark NORYL 73l/SI has been found excellent for the purpose.

In the forms of the invention as shown, each of the wedges is provided with a plurality of upstanding bumps on opposite parallel flat faces thereof, and the grooves into which these wedges are forced are of a width such that the bumps will come into interfering relation with the side surfaces of the grooves, but of a dimension so that the plastic groove sides and bumps will regain their original shape should these plastic wedges be removed therefrom.

IN THE DRAWINGS FIG. I is a back elevational view of a stretcher frame for artists canvas made according to a first form of the invention and with an artists canvas stretched thereon;

FIG. 2 is an enlarged elevational view of a part of the frame and canvas as seen in FIG. 1 but taken generally on the line 22 in FIG. 3;

FIG. 3 is an enlarged sectional view taken on the line 3-3 in FIG. 1;

FIG. 4 is an enlarged sectional view taken on the line 4-4 in FIG. 1;

FIG. 5 is an enlarged sectional view taken on the line 5-5 in FIG. 1;

FIG. 6 is an enlarged elevational view of a rivet-like fastener as disclosed in FIG. 5;

FIG. 7 is an enlarged sectional view taken on the line 7-7 in FIG. 1;

FIG. 8 is a composite top plan and edge view of a plastic wedge used in connection with the invention;

FIG. 9 is a top edge view of a fragment of a stretcher made in accordance with a second form of the invention; and

3. FIG. is a fragmentary, sectional view of the stretcher frame of FIG. 9 taken on the line 10-l0 in that FIGURE.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1 through 8, in a first form of the invention, a stretcher frame for artists canvas includes two horizontally extending stretchers 22 and 24- and two vertically extending stretchers 26 and 28as illustrated in FIG. 1. The stretchers are viewed from the backside, and the canvas positioned on those stretchers is indicated at 30.

Each stretcher is provided with a tongue and a groove at each end thereof to match or mate with an adjacent stretcher in right angular relationship thereto. A tongue 32 on horizontally extending stretcher 22 and a tongue 34 on vertically extending stretcher 28 are perhaps best illustrated to the right of FIG. 2. A similar tongue, also designated 32, is situated on the left end of the stretcher 22 as seen in FIG. 2 and in FIG. 3. This tongue 32 is in overlying adjacent, contacting relationship to a tongue 36 on the upper end of stretcher 26. This tongue 36 ofstretcher 26 fits into a groove 38 in stretcher 22, while the tongue 32 of the horizontal stretcher 22 fits into a groove 40 in vertical stretcher 26. See FIG. 3.

In order to fit universally in end to end relationship, the tongue on one end of each stretcher, for example, to the right end of stretcher 22 in FIG. 2, is situated on top of its own groove 38; while the tongue on the other end of each stretcher, for example, the tongue 32 to the left on stretcher 22 is situated underneath its corresponding groove 38 as seen in that figure.

Each groove, in addition to being deep enough to receive the entire mating tongue from an adjacent stretcher, is also deep enough to receive a wedge 42 which is designed to be used to force the tongue away from the bottom of the groove in a manner to be described. The camming surface on which wedge 42 operates is perhaps most clearly seen in FIG. 2 where the stretcher including a portion of tongue 32 have been broken away to reveal groove 38 and bottom groove camming surface 44 thereof.

Each wedge 42 includes a pair of diverging camming surfaces 46,46 and a wedge driving surface 48 situated in normal relationship to one of the converging surfaces 46. Each wedge is further defined by flat, parallel spaced-apart surfaces 50,50, each of which are provided with a plurality of upstanding protrusions or bumps 52. i

In accordance with the first form of the invention, each of the four stretchers are provided with inwardly diverging fastener-receiving openings 54 which extend clear through the stretcher from an outside edge 56 to an inside edge 58 thereof.

When it is desired to position a piece of canvas over the stretcher frame of the invention, the side of the canvas which is to be painted on is laid face down on any flat surface and the frame laid on top of the canvas. Outer edges of the canvas are turned up around each of the outer edges 56 of the stretchers, and rivet-like fasteners 60 are forced down through the canvas in alignment with and into retained relationship to each of the fastener-receiving openings 54.

One of these fasteners 60 is illustrated in elevation in FIG. 6, and includes a head 62, a bifurcated shank 64, and a pair of part-conical, canvas-piercing fingers preparatory to forcing it down through the canvas and into the fastener-receiving opening 54 is best illustrated.

in FIG. 5..The positioning of these fasteners 60 in the openings 54 and through the seen in FIG. 2. g

With the canvas fastened around all four sides ofthe frame, it must then be stretched to achieve the tension in the canvas needed or desired by an artist in the performance of his work. This is accomplished by inserting wedges 42 in each of the grooves 38 and 40 between the ends of the tongues of the adjacent stretchersand the bottom groove camming surface 44. of such; grooves. The wedges are then moved in direction'to-.

ward the outside of the frame one after the other and a little bit at a time to achieve the desired tensioning of the canvas and until the partsare in some such position as is seen in FIG. 1, for example. After the canvas has been sized or after considerable paint has been applied to it, additional tensioning may be desired, and the process will then be repeated.

In order to hold the wedges 42 in place, the overall dimension from the top of the bumps on one of the side surfaces 50 to the top ofthe bumps on the other side surface 50 of the wedge is .somewhatgreater than the]. distance between the defining side walls of the grooves 38 and 40. Thus when the wedges are pushed and tapped or otherwise driven into these grooves, there is I V a binding, interfering fit due to deformation of the? bumps and of the sides of thegrooves under the influ-;

ence of the bumps. The amount of the interference will be such that the wedges will hold firmly in pl ace until forceably,manually or otherwise loosenedgbut'will be such that both the bumps and the side surfaces ofthe grooves will come back. to their normal shape after the 3 I wedges have been removed from the grooves.

Once a painting on a canvas has been finished, it is I Y often positioned within a picture frame, and the picture frame and the canvas frame and canvas become an operational unit useful in displaying the picture on the canvas. Whether or notsuch an ornamental picture frame is added to a frame and canvas, such canvases are often supported on vertical walls for the purpose of displaying the picture on the canvas. For that purpose,

and useful either with or ;without an ornamental picture I frame, a picture hanger has been provided. This hanger is illustrated in FIGS. land 4, and consists of a pair of upstanding studs 72,72 of sizeand configuration to fit snugly in two of the fastener-receiving openings 54 through the inside edge 58 of an upper stretcher 22. Each of these studsextends upwardly from a flat horizontal platform 74. A hanger bar 76 is connected to and extends upwardly from opposite ends; of plat- 7 form 74. The hanger bar is provided with scallops or notches 80 along a bottom edge of a horizontally extending portion thereof. In use, the hanger 70 will be inserted into two of the fastener-receiving openings 54 which bridge the center of gravity of the stretcher and the frame, and a nail .78 or screw or other fastenerex-' l I tending out from a wall 79 where theframe isto be .dis-- played will be set into the proper notch to achieve proper balance of the picture.

Because the strain on .the rivet-like fasteners 60 due to theten sion in the canvas is transverse to the axis of 7 these fasteners, there is little or no tendency. for the fa's canvas 30 is perhaps best. I

teners to pull out, and particularly where the frame and canvas are mounted in an ornamental frame which covers the outer edges of the frame of the invention, the

canvas will stay forever permanently fixed in the frame if that is what is desired.

Conversely, should the artist decide thatthe canvas is not to be saved, a simple application of a pen knife or similar implement under the head 62 of each fastener 60 will cause that fastener to come out of its opening 54 and the canvas will thus be released. This structure, including the stretchers of the frame and the fasteners, can be used over and over again indefinitely without appreciable wear on either of these parts. Even the same piece of canvas 30 can be replaced time after time if this should for some reason be desirable by utilizing the same pierced fastener openings in the canvas each time.

Referring now to H68. 9 and 10, in accordance with a second form of the invention, the stretchers and wedges are, in all particulars except the means of fastening the canvas on to them, identical with the stretchers and wedges discussed in connection with the first form of the invention. However, in place of'providing fastener-receiving openings through the stretchers, the stretchers are formed with channel-like openings 82 open to the outside edges 56 thereof. These channels are completely filled with hard felt or soft plastic strips 84. These strips are of a nature such that they will hold the shank of a headed nail or the shanks of a staple which is forced into them, but will completely refill and obliterate such a hole after the nail or staple has been removed.

To use the artists canvas stretcher frame of the second form of the invention, the frame is assembled in the manner set out in connection with the first form of the invention, and is set face down on the back side" of a canvas to be mounted. The outer edges of the canvas are folded around the outer edges 56 of each stretcher, and headed nails or staples 86 are driven down through the canvas and into the felt strips 84. When this has been accomplished on all four sides, the canvas is then stretched using wedges 42 as explained in connection with the first form of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In combination with an artists canvas, a stretcher frame for stretching said canvas, said frame having four elongated stretchers, two each being the same length, and each having a tongue and a groove at each end of configuration to fit together tongue and groove with said adjacent stretchers to form a flat, rectangular structure adapted to receive said canvas, each of said grooves when assembled with one of said tongues continuing past said tongue to provide an inwardly diverging, wedge-receiving slot bounded by the end of said tongue, two flat parallel groove-defining walls and a camming surface, said walls and surface being constitutedas part of said stretcher, said slot being open to an inside edge of said stretcher, said slot being open to an inside edge of said stretcher, means for fastening said canvas to outside edges of each of said stretchers, and in combination with substantially flat wedges of configuration to fit into said slots and having edges of configuration to tend to move said tongues away from said camming surfaces as said wedges are forced farther into said slots; the improvements including:

A. constituting each of the stretchers and each of the wedges of suitable plastic material; I B. at least one substantially'flat surface of 'each of said wedges being provided with a plurality of spaced-apart, upstanding bumps thereon, the overall thickness of said. bumps and of each of said wedges being sufficiently greater than the transverse dimension between the two groove-defining ,walls of its associated slot so that the wedge will be retained in place by said walls as it is and after it has been forced into said slot to achieve the tensioning of said canvas; and C. the dimensioning of the wedges and bumps and of the groove-defining walls of the slots and the physical properties of the plastic of the stretchers and of the plastic of the wedges being such that the slot walls and bumps will deform when said wedges are forced into said slots and will completely regain their original shape and dimensions shortly after said wedges are removed from said slots. 2. The combination as specified in claim 1 wherein said plastic material of said stretchers and the plastic material of said wedges is constituted as a plastic material having the same physical properties as a material identified by the trademark and identification numbers NORYL 731/81.

3. In combination with an artists canvas, a stretcher frame for stretching said canvas, said frame having four elongated stretchers, two each being the same length, and each having a tongue and a groove at each end of configuration to fit together tongue and groove with said adjacent stretchers to form a flat, rectangular structure adapted to receive said canvas, each of said grooves when assembled with one of said tongues continuing past said tongue to provide an inwardly diverging, wedge-receiving slot bounded by the end of said tongue, two flat parallel groove-defining walls and a camming surface, said walls and surface being constituted as part of said stretcher, said slot being open to an inside edge of said stretcher, means for fastening said canvas to outside edges of each of said stretchers, and in combination with substantially flat wedges of configuration to fit into said slots and having edges of configuration to tend to move said tongues away from said camming surfaces as said wedges are forced farther into said slots; the improvements wherein said means for fastening said canvas to outside edges of each of said stretchers includes a plurality of spaced apart fastener-receiving openings provided in each stretcher and open to said outside edge thereof, and a plurality of rivet-like fasteners having shank portions of configuration to penetrate through said canvas and to extend into one of said openings, and having an enlarged rivet-like head adapted to hold said canvas to said outside edge of said stretcher when said fastener is in position in said opening.

4. The combination as specified in claim 3 wherein fastener-receiving openings are of increasing cross sectional dimension from position adjacent an outside edge of said stretcher toward an inside edge thereof.

5. The combination as specified in claim 1 wherein said means for fastening said canvas to outside edges of each of said stretchers includes a plurality of spaced apart fastener-receiving openings provided in each stretcher and open to said outside edge thereof, and a plurality of rivet-like fasteners having shank portions of configuration to penetrate through said canvas and to extend into one of said openings, and having an enlarged rivet-like head adapted to hold said canvas to said outside edge of said stretcher when said fastener is in position in said opening.

6. The combination as specified in claim wherein fastener-receiving openings are of increasing cross sectional dimension from position adjacent an outside edge of said stretcher toward an inside edge thereof.

7. In combination with an artists canvas, a stretcher frame for stretching said canvas, said frame having four elongated stretchers, two each being the same length, and each having a tongue and a groove at each end of configuration to fit together tongue and groove with said adjacent stretchers to form a flat, rectangular structure adapted to receive said canvas, each of said grooves when assembled with one of said tongues continuing past said tongue to provide an inwardly diverging, wedge-receiving slot bounded by the end of said tongue, two flat parallel groove-definingwalls and a camming surface, said walls and surface being constituted as part of said stretcher, said slot being open to an inside edge of said stretcher, means for fastening said canvas to outside edges of each of said stretchers, and in combination with substantially flat wedges of configuration to fit into said slots and having edges of configuration to tend to move said tongues away from said camming surfaces as said wedges are forced farther into said slots; the improvements wherein said means for fastening saidcanvas to outside edges of each said stretcher includes a channel-like opening extending longitudinally substantially the entire length of each stretcheryand a plurality of nail or staple-like fas- 5 I teners adapted to pierce through said canvas and ex-,

tend into said material-filled channel-like openingsto retain said canvas in contact with outside edges of each 7 of said stretchers.

8. The combination as specified in claim 1 wherein saidmeans for fastening said canvas to outside edges of each said stretcher includes a channel-like opening extending longitudinally substantially the entire length of an outside edge portion of each of said stretchers, a material suitable for retaining the shank of a nail-like fastener when such shank is forced therein, said material completely filling each such channel-like openingon each stretcher; and a plurality of nail or staple-like fasteners adapted to pierce through said canvas and extend into said material-filled channel-like openings to retain said canvas in contact with outside edges of each of said stretchers. 

1. In combination with an artist''s canvas, a stretcher frame for stretching said canvas, said frame having four elongated stretchers, two each being the same length, and each having a tongue and a groove at each end of configuration to fit together tongue and groove with said adjacent stretchers to form a flat, rectangular structure adapted to receive said canvas, each of said grooves when assembled with one of said tongues continuing past said tongue to provide an inwardly diverging, wedgereceiving slot bounded by the end of said tongue, two flat parallel groove-defining walls and a camming surface, said walls and surface being constituted as part of said stretcher, said slot being open to an inside edge of said stretcher, said slot being open to an inside edge of said stretcher, means for fastening said canvas to outside edges of each of said stretchers, and in combination with substantially flat wedges of configuration to fit into said slots and having edges of configuration to tend to move said tongues away from said camming surfaces as said wedges are forced farther into said slots; the improvements including: A. constituting each of the stretchers and each of the wedges of suitable plastic material; B. at least one substantially flat surface of each of said wedges being provided with a plurality of spaced-apart, upstanding bumps thereon, the overall thickness of said bumps and of each of said wedges being sufficiently greater than the transverse dimension between the two groove-defining walls of its associated slot so that the wedge will be retained in place by said walls as it is and after it has been forced into said slot to achieve the tensioning of said canvas; and C. the dimensioning of the wedges and bumps and of the groovedefining walls of the slots and the physical properties of the plastic of the stretchers and of the plastic of the wedges being such that the slot walls and bumps will deform when said wedges are forced into said slots and will completely regain their original shape and dimensions shortly after said wedges are removed from said slots.
 2. The combination as specified in claim 1 wherein said plastic material of said stretchers and the plastic material of said wedges is constituted as a plastic material having the same physical properties as a material identified by the trademark and identification numbers NORYL 731/SI.
 3. In combination with an artist''s canvas, a stretcher frame for stretching said canvas, said frame having four elonGated stretchers, two each being the same length, and each having a tongue and a groove at each end of configuration to fit together tongue and groove with said adjacent stretchers to form a flat, rectangular structure adapted to receive said canvas, each of said grooves when assembled with one of said tongues continuing past said tongue to provide an inwardly diverging, wedge-receiving slot bounded by the end of said tongue, two flat parallel groove-defining walls and a camming surface, said walls and surface being constituted as part of said stretcher, said slot being open to an inside edge of said stretcher, means for fastening said canvas to outside edges of each of said stretchers, and in combination with substantially flat wedges of configuration to fit into said slots and having edges of configuration to tend to move said tongues away from said camming surfaces as said wedges are forced farther into said slots; the improvements wherein said means for fastening said canvas to outside edges of each of said stretchers includes a plurality of spaced apart fastener-receiving openings provided in each stretcher and open to said outside edge thereof, and a plurality of rivet-like fasteners having shank portions of configuration to penetrate through said canvas and to extend into one of said openings, and having an enlarged rivet-like head adapted to hold said canvas to said outside edge of said stretcher when said fastener is in position in said opening.
 4. The combination as specified in claim 3 wherein fastener-receiving openings are of increasing cross sectional dimension from position adjacent an outside edge of said stretcher toward an inside edge thereof.
 5. The combination as specified in claim 1 wherein said means for fastening said canvas to outside edges of each of said stretchers includes a plurality of spaced apart fastener-receiving openings provided in each stretcher and open to said outside edge thereof, and a plurality of rivet-like fasteners having shank portions of configuration to penetrate through said canvas and to extend into one of said openings, and having an enlarged rivet-like head adapted to hold said canvas to said outside edge of said stretcher when said fastener is in position in said opening.
 6. The combination as specified in claim 5 wherein fastener-receiving openings are of increasing cross sectional dimension from position adjacent an outside edge of said stretcher toward an inside edge thereof.
 7. In combination with an artist''s canvas, a stretcher frame for stretching said canvas, said frame having four elongated stretchers, two each being the same length, and each having a tongue and a groove at each end of configuration to fit together tongue and groove with said adjacent stretchers to form a flat, rectangular structure adapted to receive said canvas, each of said grooves when assembled with one of said tongues continuing past said tongue to provide an inwardly diverging, wedge-receiving slot bounded by the end of said tongue, two flat parallel groove-defining walls and a camming surface, said walls and surface being constituted as part of said stretcher, said slot being open to an inside edge of said stretcher, means for fastening said canvas to outside edges of each of said stretchers, and in combination with substantially flat wedges of configuration to fit into said slots and having edges of configuration to tend to move said tongues away from said camming surfaces as said wedges are forced farther into said slots; the improvements wherein said means for fastening said canvas to outside edges of each said stretcher includes a channel-like opening extending longitudinally substantially the entire length of an outside edge portion of each of said stretchers, a material suitable for retaining the shank of a nail-like fastener when such shank is forced therein, said material completely filling each such channel-like opening on each stretcher; and a plurality of nail or staple-like fasteners adapted to pierce through said canvas aNd extend into said material-filled channel-like openings to retain said canvas in contact with outside edges of each of said stretchers.
 8. The combination as specified in claim 1 wherein said means for fastening said canvas to outside edges of each said stretcher includes a channel-like opening extending longitudinally substantially the entire length of an outside edge portion of each of said stretchers, a material suitable for retaining the shank of a nail-like fastener when such shank is forced therein, said material completely filling each such channel-like opening on each stretcher; and a plurality of nail or staple-like fasteners adapted to pierce through said canvas and extend into said material-filled channel-like openings to retain said canvas in contact with outside edges of each of said stretchers. 